1. Field of the Invention
The present invention relates to a system and method for reading two-dimensional images. More particularly, the present invention relates to a system and method for reading a two-dimensional images, such as fingerprints, signatures, and photographs, using an optical scanning head and a data compression algorithm.
2. Description of Related Art
Two-dimensional images are capable of carrying valuable information for use in various applications. For example, two-dimensional images may provide personal identification (e.g., by a fingerprint) or a record of, for example, a person""s medical history. Therefore, two-dimensional images are extremely valuable for carrying and conveying information and data.
Recently, optical scanners and readers have been developed that can capture and decode two-dimensional images. Such optical devices scan or obtain a video xe2x80x9cpicturexe2x80x9d of the two-dimensional image and process it using data compression techniques to obtain decoded data representative of the image. This data can then be used in comparing the two-dimensional image to some known data generated from a known image to determine whether the decoded data and known data match. The known data can be encoded in a two-dimensional barcode symbology representative of the known image.
Manipulation of data derived from two-dimensional images is useful in a number of applications. For example, when a person opens a bank account, the bank can scan the person""s fingerprint and decode that scanned image into data representative of the person""s fingerprint (xe2x80x9cstored dataxe2x80x9d), which is kept on file by the bank and by other institutions. Moreover, the stored data can be encoded onto a card that provides access to automatic teller machines (ATMs). When the person wants to gain access to money stored in an ATM, the person is asked to insert his or her ATM card into the ATM and place his or her fingertip in contact with a sensor-containing glass in which the contrast is controlled electronically in front of an optical scanner located at the ATM. The optical scanner scans and decodes the person""s fingerprint to obtain features (data) representative of the fingerprint (xe2x80x9cnew dataxe2x80x9d). This new data can then be compared to the stored data kept on file with the bank or obtained from the ATM card. If the new data matches the stored data, the person is given access to the ATM; if not, access is denied. The stored data can be encoded onto the ATM card by scanning the person""s fingertip and decoding the scanned information into a two-dimensional barcode symbology that represents the person""s fingerprint.
Conventional optical scanners for use with two-dimensional images are very expensive, however, due to the high cost of the components necessary to build such scanners. In conventional optical scanners for two-dimensional images, the most expensive component is the image sensor, which comprises a charge coupled device (CCD). Accordingly, using CCDs for two-dimensional image sensing renders this technology not cost-effective for applications where, for example, a large number of scanners are needed by a user with a relatively small business.
Therefore, a need exists for a system and method for scanning and decoding two-dimensional images that permits the use of both a CCD sensor and sensor that is less expensive than a CCD sensor, that can perform data compression to process the image after scanning, and that can generate a barcode symbology representation of the processed image.
Accordingly, the present invention is directed to a system and method for scanning and decoding a two-dimensional image using an inexpensive optical scanning head that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the system and method particularly pointed out in the written description and claims hereof, as well as the appended drawings.
In an exemplary embodiment, the optical scanning device comprises a sensor for capturing the two-dimensional image and an LED array for projecting an emitted light towards the target, i.e., the two-dimensional image, all of which are mounted on a printed circuit board (PCB). The LEDs may be used for two purposes: first, to set the optimum distance of the target to the lens system, and, second, to illuminate the target during image acquisition. The LEDs used for these two functions may be the same sets or different sets of LEDs within the array. The LED array includes a plurality of LEDs, with each LED being oriented to emit light at a non-zero angle with respect to a center line running perpendicular to the front of the PCB. The LED orientation is selected to cause the light to diverge as it exits the front of the device, creating a wider beam at the target than at the front of the exit window of the device. One method by which this may be achieved is by orienting each LED at an angle different from any of the other LEDs. Another method is to orient the LEDs on either side of the centerline at complementary non-zero angles, i.e., the beam from each LED will cross the centerline at some point on its way out of the device. The sensor may also include optics disposed forward of the LED array for focussing and/or diffusing the emitted light at the target. Optics are also provided for receiving and focussing the light reflected from the target. The sensor further includes an image detector, either a CMOS (complementary metal-oxide-silicon) detector or a CCD detector, for detecting at least a portion of the light reflected from the two-dimensional image. An illumination detector comprising a photodiode or phototransistor may be included for sensing the reflected light from the target to establish exposure time to be used during image acquisition, and to determine if supplemental light is needed. A processor receives the output of the image detector for processing the sensed two-dimensional image to obtain an electrical image signal and the output of the illumination detector to control exposure and supplemental illumination, if needed. The processor, which may be a microprocessor or microcomputer, may incorporate software capability for automatic gain control, automatic exposure control, automatic black level control and automatic calibration, as well as control of the light sources and detectors. For handling large quantities of data as will be required in certain applications, the software for controlling the optical scanning device may further include a compressor function for compressing the electrical image data, the compressor employing a compression algorithm to obtain compressed image data. The software of the optical scanning device finally comprises a decoder for decoding the image signal to obtain image data representative of the two-dimensional image.
In many applications, ambient light may be sufficient for illuminating the target to permit the detector to generate a high quality image signal, however, in low light conditions, the same detector may need a light source to supplement the ambient light. To determine whether supplemental light is needed, the photodiode or phototransistor can be located close to the detector to determine how much light is actually impinging upon the detector. The output of this photodetector is amplified and converted to a digital signal, then fed to the scanning device""s controller to control the amount of supplemental illumination provided by the LED light sources.
In a first embodiment, the present invention is a system and method for capturing a new two-dimensional image which may be compared to stored data representative of a known two-dimensional image. The system comprises the optical scanning device described above for capturing a new two-dimensional image. The comparison operation is provided by a second processor to determine if the new image data matches the stored data.
In still another aspect, the present invention is a system and method for generating a two-dimensional image from a scanned target which may then be compared to stored data representative of a known two-dimensional image. The system comprises a sensor as previously described for capturing the new two-dimensional image, however, the emitted light can either be used to illuminate the target image or it can be focused to form a frame identifying the field of view of the sensor. A cylindrical lens system disposed forward of the LED array focusses the emitted light into a line of light. Depending upon the orientation of the cylindrical lens(es), a line may be formed to illuminate the target two-dimensional image within a field of view of said sensor so that a reflected light is reflected from the new two-dimensional image. Alternatively, a vertical orientation of the cylindrical lens(es) provides two vertical lines of light for framing the field of view to allow the user to aim the sensor at the target, and the target image is illuminated by ambient light. Either of the cylindrical lens applications can also be achieved by directing an LED (or laser diode) toward a cylindrical mirror which reflects a plane of light that can provide a line of light at the target.
In the above described systems, the optical scanner may include optics for indicating the area of the target that falls within the field of view so that the device can be correctly aimed at the target image, or so that the target image can be moved to be within the device""s field of view, i.e., a xe2x80x9cframe locatorxe2x80x9d. In addition to the vertically-oriented cylindrical lenses to create frame lines using the LED light, one or more laser diodes may be provided alone or in combination with diffraction gratings, binary optics, beam splitters and/or mirrors to generate lines or points of light to indicate the location of the edges of the field of view of the detector. The frame locator may be used alone, with only ambient light providing the means for scanning the target, or, in combination with the LEDs where the entire field of view is illuminated. Where the laser provides edge markers as part of the frame indicator function, typically, there are four points of light, defining the four corners of a square or rectangular field of view.